SAN FRANCISCO / Two views of mass confusion

As the debate over Critical Mass and the clash between bicyclists and a minivan driver rages, two widely varying eyewitness versions of what happened Friday night in Japantown have emerged.

It could be a case of a terrified family whose minivan was surrounded by angry bicyclists who rode their bikes in circles around the vehicle, harassed the driver and then pummeled the van, smashing a rear window and inflicting $5,300 in damage.

Or it's a situation that spun out of control when a frustrated driver accelerated recklessly through a crowd of Critical Mass cyclists, struck one and continued driving until bike riders surrounded the minivan and police arrived.

Who's right and who's wrong is a matter of debate on blogs, in coffee houses and over dinner tables around the Bay Area. Is someone lying, or did different people simply see the scenario unfold differently?

"Everybody's perspective is different," said Kate McCarthy, a Critical Mass rider who said she witnessed the event. "Maybe the cyclists saw different things. There was a lot going on. It was kind of a chaotic situation."

San Francisco police said they could not release their report on the incident because the case is still under investigation. But their earlier characterizations of the event reflect the minivan driver's account.

Susan Ferrando, the Redwood City mother who was driving the minivan, recounted her version in an interview Thursday afternoon. She denied that she hit or ran over a bicyclist or his bike -- and decried those accusations as "ludicrous."

After finding herself in the middle of the ride, she said, she nervously made her way through the bicyclists, carefully watching them. Some rode very close to the car, and yelled at her, then began circling it. One, she said, rammed the minivan, but did not fall. She said she didn't know if this was the same person who bicyclists say was hit.

"Their lies are just in support of their negative tactics," she said. "It undermines the message they're trying to get across."

McCarthy said the incident nevertheless underscores the message that bicyclists are unsafe on San Francisco streets.

McCarthy said she split off from the main Critical Mass ride as it hit Japantown, and started heading home up Post Street with four other cyclists. The minivan was behind her as it weaved its way through an undetermined number of cyclists, she said. Then it hit a bicyclist near Octavia Street, she said. He fell to the ground, McCarthy said, and the bike went under the front of the minivan. The driver, she said, didn't stop until four cyclists got in front.

Nobody disputes that the situation at the corner of Post and Gough streets spun out of control and that the minivan ended up with a broken window and other damage, perhaps inflicted with bicycles. Their differing versions of what led to the confrontation are understandable, according to Daniel Schacter, a Harvard University psychology professor who has written books about the shortcomings of memory and eyewitness accounts.

"The mind is not a video recorder," he said. "People remember what they see differently."

Witnesses focus on different things, he said, some see more details than others and some recall events more accurately. Some may confuse what they witnessed with something that happened in another incident or get the order in which events occurred mixed up, he said, especially when trauma is involved.

In incidents when witnesses may be attempting to interpret someone's motives, Schacter said: "You have people bringing different assumptions and backgrounds, and their memory is being created through those assumptions and backgrounds. The things we know affect how we see things."